A student uses a red hosepipe to make a solar water heater - Edexcel - GCSE Physics - Question 2 - 2018 - Paper 1

During the day, as the sun rises and shines on the solar heater, the temperature of the water in the hosepipe increases. This is due to the absorption of sunlight by the hosepipe, which heats the water. The temperature will continue to rise until it reaches a maximum when the sun is at its peak. As the sun sets, the temperature of the water will gradually decrease as it loses heat to the surrounding environment. Therefore, the overall trend is a rise in temperature during daylight hours, followed by a decline as night approaches.

The efficiency of the heater can be calculated using the formula:

$\text{Efficiency} = \frac{\text{Energy absorbed}}{\text{Solar energy incident}} \times 100$

In this case, the energy absorbed by the heater can be found by subtracting the reflected energy from the incident energy:

( \text{Energy absorbed} = 15000 J - 6000 J = 9000 J )

Now substituting into the efficiency formula:

$\text{Efficiency} = \frac{9000 J}{15000 J} \times 100 = 60\%$

Thus, the efficiency of the heater is 60%.